Neuroblastoma is a disease that frequently occurs principally in children of five years old or younger, and of which the frequency is the highest among solid tumors in infants. As to genetic features associated with neuroblastoma, amplification of MYCN oncogene, deletion of chromosome 1p and the like are known. In particular, the current therapy is not effective for many of cases of patients of one year old or older having highly advanced tumors, or cases with the above-mentioned amplification of MYCN oncogene or deletion of chromosome 1p. Although the relationship between the amplification of MYCN oncogene (found in about 20% of the disease cases) and neuroblastoma was suggested in the mid-1980s, there has been no report on a molecule that surely has an important function specific for neuroblastoma since then, and almost nothing has been elucidated concerning the molecular mechanism of the tumor. Although there is an urgent need for establishment of a method of treating neuroblastoma, the above has been a principal cause that impedes development of a new treatment method (Non-patent Document 1).
The present inventors produced an ARID3b knock-out (KO) mouse during the course of studies on differentiation-induction of mesodermal cells and mesenchymal cells using an in vitro differentiation system for mouse embryonic stem (ES) cells. ARID3b is a molecule of unknown function of which the expression pattern is similar to that of platelet-derived growth factor (PDGF) receptor molecule. Based on the observation that most of PDGFRα-positive cranial mesenchymal cells which were considered to be derived from neural crest cells disappeared in the KO mouse, it was found that this molecule is indispensable for differentiation, growth and maintenance of mesenchymal cells. The ADID3b molecule is a protein that belongs to a group of molecules that have a DNA-binding motif called AT rich interacting domain. The gene encoding this protein forms a subfamily with another gene for ARID3a. The gene encoding human ARID3b was cloned, and ARID3b was shown to be a protein that binds to retinoblastoma gene product (Rb) (Non-patent Document 2), although its function has been unknown.    Non-patent Document 1: Brodeur, G. M. et al., Nature Reviews Cancer, 3:203-216 (2003)    Non-patent Document 2: Numata, S. et al., Cancer Res., 59:3741-3747 (1999)